* The body segmented, the segments usually grouped in two or three rather distinct regions - making them highly mobile. 

* Paired segmented appendages (from which the phylum gets its name) - making them ambulate & walk easily. 

* Bilateral symmetry - making them relate to the environment quite easily. 

* A chitinous exoskeleton, which is periodically shed and renewed as the animal grows - making them resistant to shock of hard objects. 

* A tubular alimentary canal, with mouth and anus - accounting for good food digestion. 

* The circulatory system an open one, the only blood vessel usually being a tubular structure dorsal to the alimentary canal with lateral openings in the abdominal region - ensures better perfusion and less chances of hemolysis due to their being highly mobile.